The aim of this study was to evaluate the theoretical fidelity and message quality for its future incorporation in just-in-time, adaptive physical activity intervention. The content of the messages and images was based on a wide variety of behavior change strategies to target validated cognitive and affective targets such as goal setting, barrier identification, enjoyment and motivation. Two studies were conducted with two separate participant populations. Experts (n=6) in the field of behavior change interventions assessed the theoretical fidelity of the messages, and the target population (n=100) rated the images and messages on their quality. Both groups of participants completed a single survey and the average ratings were calculated for each category and construct. The expert population ratings showed a moderate-to-high level of theoretical fidelity of the messages. The target population indicted a moderate level of message quality. Based on the feedback from the target population, several defining characteristics emerged as either highly beneficial to interest and identification or detrimental to the engagement of the population. This knowledge was used to modify the images and messages with low ratings, and increase the overall levels of interest, identification, and autonomy in the content utilized for the future physical activity intervention
